RUTHFULLY YOURS

By CHIP CUMMINS And ALISTAIR MACDONALD

DUBAI—Soon after the January assassination of a top Palestinian official here, Dubai police stumbled onto what looked like a big break in the case.

They linked a white-haired man with glasses to several suspects caught on security cameras preparing for the murder. Most of the suspects in the case had carried forged passports, but this man had a real British one. It identified him as 62-year-old Christopher Lockwood.

The assassination of Hamas leader Mahmoud al-Mabhouh in January 2010 in a Dubai hotel evoked mixed reactions around the world. But after a few early leads, the Dubai police have found the trail has gone cold.

A cellphone linked to him had recently been switched on in France. U.K. authorities found his London address. They also discovered that in 1994, he had changed his name from Yehuda Lustig. Mr. Lustig, they determined, was born in Scotland to a Jewish couple from what was then British-controlled Palestine.

The findings raised hopes of nabbing one of the orchestrators of the hit, possibly providing proof for accusations by Dubai police that Israel’s intelligence agency Mossad was behind it.

But just as quickly, the trail went cold, a Wall Street Journal examination of the case shows.

British police staked out the London residence, but Mr. Lockwood never showed up, according to investigators. They didn’t find him in France, either. More troubling still, Mr. Lockwood’s prior identity looked to be a ruse: Mr. Lustig was reported killed in 1973 as a young Israeli soldier during the Yom Kippur War, according to official Israeli obituaries. That left investigators no closer to finding out who Mr. Lockwood really is.

Associated PressFather of Mahmoud al—Mabhouh with photo of his murdered son

It has been more than eight months since the murder of top Hamas official Mahmoud al-Mabhouh, whose body was found in a Dubai hotel room Jan. 20. Quick work by Dubai police and a diplomatic furor over the use of dozens of forged passports in the case fed early optimism that at least some of the 30-plus suspects would be found. But a string of apparent dead ends has frustrated international investigators, lengthening the odds that anyone will be caught or that definitive proof of Mossad involvement will emerge.

And despite an initial burst of tough talk from various governments, some international investigators are concerned that politics may be hampering cooperation from some governments that support Israel.

Time isn’t on the side of Dubai, one of seven emirates that make up the United Arab Emirates. International investigators have been operating under the assumption that, if Israel is behind the crime, the suspects already may have made their way back to Israel, where they’ll be safe from extradition.

“The longer these investigations go on, the more enthusiasms dwindle and the more time for a security service to cover tracks and bury things,” says Nick Day, a former operative in the U.K.’s MI5 security service who isn’t involved in the probe.

Israel isn’t cooperating in the probe. It has said there’s no evidence linking Mossad to the murder of Mr. Mabhouh, one of the founders of the military wing of Hamas, the Islamist Palestinian group that Washington, London and Israel designate as a terror organization. Spokesmen for Israeli Prime Minister Benjamin Netanyahu and the Israeli foreign ministry declined to comment for this article.

Early this year, Dubai’s police chief said he was “99%” sure of Mossad involvement. Still, investigators on the case, including those in the U.A.E., say they are working with an open mind. Early on, Dubai detained two Palestinians, raising the possibility that the killing was orchestrated by Palestinian rivals to Mr. Mabhouh. Since then, several allies of Israel have publicly blamed the country for forging many of the passports used by suspects in the case. That has reinforced the widespread suspicion of Israeli involvement.

Dubai investigators remain hopeful, but are coming to terms with the possibility that the probe could drag on for years. “They realize this might be a long process,” says one person familiar with the probe.

At a press conference in February announcing the first batch of suspects, Dubai’s police chief, Lt. Gen. Dahi Khalfan Tamim, vowed to pursue the suspects “until the end of time.”

InterpolSuspect Christopher Lockwood.

The lead on Mr. Lockwood isn’t the only one to fizzle.

Two suspects, traveling with forged passports, appeared to have fled to the U.S. shortly after the killing. Their passport details showed up in a U.S. border-control system that collects electronic manifests of international flights and screens them against passenger watch lists, according to people familiar with the probe and to investigation documents reviewed by the Journal. That suggested the suspects had boarded planes bound for the U.S. The information was passed to international investigators involved in the case, raising hopes of a capture.

But the U.S. Department of Homeland Security has since said it doesn’t have records of the two suspects in its system.

Prosecutors in Cologne, Germany, sought an Israeli man on espionage charges related to the murder. The man was extradited from Poland on a lesser charge of document fraud. In August, a German court released him on bail. A spokesman for the prosecutor’s office said Dubai hadn’t provided enough evidence to justify holding him any longer.

The man flew to Israel within hours of his release. By leaving Germany, he revived the German arrest warrant on espionage charges, a prosecution spokesman said. But the warrant is unlikely to be enforced in Israel.

As for the two Palestinians detained in Dubai shortly after the killing, one had been caught on an airport security camera appearing to pass off an item to one of the suspects. But the men haven’t yet provided any meaningful leads, according to people familiar with the probe.

No other arrests have been made.

Israeli Ministry of DefenseSuspect Christopher Lockwood once assumed the identity of dead Israeli soldier Yehuda Lustig, above.

The U.A.E. was well-positioned to get investigative cooperation from foreign governments. It has emerged as a Western-leaning Arab powerhouse and important bulwark against Iran. It enjoys strong ties with the U.S. and many Western nations, and Washington has courted it in its global fight against terror financing.

The large-scale passport fraud, blamed on Israel, sparked widespread anger, especially in Europe, raising the prospect that governments would make the investigation a priority.

“This has gone beyond the pale,” says one European-based official familiar with the case. The forgeries, he says, raised the question: “Does Israel have to play by any rules, or does it always get a special exemption?”

But from the start, some international investigators and officials were concerned that politics might interfere. They wondered how much help would be forthcoming from countries with strong ties to Israel.

The U.S. and many Western nations have for decades quietly worked with Mossad and other Israeli agencies, benefiting from their intelligence gathering in the Middle East and beyond. The Dubai investigation gathered steam just as Washington was trying to repair relations with Israel, strained by policy clashes earlier in the year over how to restart Mideast peace talks, now under way between Israel and the Palestinians.

Two senior American officials acknowledge the case is unusually sensitive because of Washington’s close ties with Israel and U.S. efforts to improve counterterrorism cooperation with U.A.E. The U.S. is cooperating with Dubai by probing financial transactions of some suspects who used U.S.-issued cash cards.

U.A.E. officials have avoided explicit criticism of other nations. After the release of the suspect by Germany, for example, the U.A.E. issued a mild rebuke, saying it was “concerned” by the decision and had asked Berlin for clarification.

British authorities took an early interest. Of the 45 passports Dubai officials say were used by 33 suspects, 19 were forged or fraudulently issued British ones. That sparked anger in London. It wasn’t the first time relations with Israel were strained over allegedly forged passports. In 1982, an Israeli embassy diplomatic pouch with fake British passports was found in a German phone booth. In 1986, Prime Minister Margaret Thatcher got an apology after British police found more Israeli-forged U.K. passports.

In late March, London publicly blamed Israel for the Dubai forgeries, but stopped short of accusing it of the killing itself. It expelled an Israeli official in protest. According to a person familiar with the case, U.K. authorities determined that the official worked for Mossad. Australia and Ireland also blamed Israel for forgeries and expelled diplomats. Israel’s foreign ministry said it regretted the expulsions, but didn’t admit wrongdoing.

Hours after the killing, Dubai officials realized they had a high-priority murder investigation on their hands. Initially, it appeared Mr. Mabhouh had died of natural causes. A bottle of blood-pressure medicine was found on the bedside table of his room in the business-class Al Bustan Rotana hotel, near the Dubai airport. There were no obvious signs of a struggle. A preliminary medical assessment at the scene suggested a sudden, natural death.

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Reuters/Dubai PoliceSecurity cameras in the hotel where top Hamas official Mahmoud al-Mabhouh was slain captured photos of various suspects.

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Reuters/Dubai PoliceSecurity cameras captured photos of various suspects.

Mr. Mabhouh’s prominence triggered extra scrutiny. A special investigative unit examined the scene more closely. Things didn’t add up, say people familiar with the probe.

Investigators couldn’t find the shirt that the hotel’s security camera showed Mr. Mabhouh wearing the night of his death. Police looked under the bed and discovered several broken slats, suggesting Mr. Mabhouh had been thrown onto the bed or held down, police concluded.

Police spent about 10,000 hours poring over footage from some 1,500 security cameras around Dubai. Using face-recognition software, electronic-payment records, receipts and interviews with taxi drivers and hotel staff, they put together a list of suspects and publicized it.

In video footage made public by the police, some of the suspects were shown donning disguises, including wigs. At one point, two suspects carrying tennis rackets shared an elevator with Mr. Mabhouh.

A camera outside a hotel caught the reflection of a white minivan with tinted windows pulling up to the building’s entrance. Several suspects approached the vehicle, then pulled back abruptly, according to people familiar with the probe.

Dubai police believe the suspects mistook the vehicle for that of a colleague, then turned back after getting a good look. That suggested to police that an accomplice might be driving a similar vehicle. After sifting through auto-registration and electronic toll-road data, they came up with a make and model, then found a similar minivan. It was rented to Mr. Lockwood.

U.K. authorities determined that the passport Mr. Lockwood used to travel to the U.A.E. was genuine. Dubai asked Interpol to post an international “wanted” notice for him.

But apart from his London address, Mr. Lockwood left little in the way of a paper trail. U.K. investigators couldn’t find any public-health records or tax information about the man, according to people familiar with the probe. He never paid a TV-license fee, mandatory in Britain for anyone who owns a set.

Investigators found other intriguing clues: Two years ago, using a British address, Mr. Lockwood shipped a blue Mercedes van from Sharjah, another emirate in the U.A.E., to Iran, according to people familiar with the probe. Someone else shipped the van to Britain.

But that lead fizzled, too. The vehicle’s registration had lapsed, and the car hasn’t been located, according to a person familiar with the case.

Investigators now believe Mr. Lockwood operated in Europe and the Middle East for years, and that he served as a facilitator to Mr. Mabhouh’s assassins, according to people familiar with the probe.

Dubai officials determined that he had flitted in and out of their city-state, according to people familiar with the probe. But their information was also scarce: a few records showing he rented a car and used a credit card at restaurants. During his last stay, he lived at a short-term, furnished apartment.

Dubai officials believe he bought ferry tickets for two suspects in the murder. Both traveled from Dubai to Iran in Aug. 2009, after what Dubai police believe was a related operation to plot the Mabhouh murder.

When investigators discovered that Mr. Lockwood was once known as Mr. Lustig, the plot appeared to thicken. Mr. Lustig’s birth certificate indicated he was born in Glasgow on Feb. 23, 1948. Mr. Lustig’s father was a veterinary student who had married in Palestine, then under British control.

Investigators figured he probably changed his name from Lustig to avoid suspicion while traveling in the Middle East, according to people familiar with the probe.

But Mr. Lustig’s military service history—described in six Israeli memorials, including an official obituary posted on the Israeli Ministry of Defense’s website—indicates the man of that name died in combat in a barrage of rocket fire in the Sinai Peninsula.

That clouded the picture—and suggests that an unknown person fraudulently used the dead soldier’s identity to obtain a British passport. Investigators appear to be back at square one in figuring out who that is.

—Joshua Mitnick, Carolyn Henson, David Crawford, Evan Perez, Rachel Pannett and Lucy Craymer contributed to this article.Write to Chip Cummins at chip.cummins@wsj.com and Alistair MacDonald at alistair.macdonald@wsj.com