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.

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.