A Hamas official who was killed in his hotel room here in January was first injected with a fast-acting muscle relaxant and then suffocated, Dubai police officials said Sunday.

The disclosure was the latest in a near-daily drip of information about the killing, which has riveted people across the Middle East and provided a rare level of detail about a political assassination widely believed to have been carried out by Israel’s intelligence service, the Mossad.

The drug, succinylcholine, is often used by doctors to administer a breathing tube, but it has also been used in killings and as a paralyzing agent before lethal injection. Investigators discovered the relaxant in the body of the Hamas operative, Mahmoud al-Mabhouh, after noticing an injection mark on his thigh, according to a forensic specialist who spoke at a news conference alongside Dubai’s deputy police chief, Khamis al-Mazeina.

“After using this drug to gain control of him, they killed him,” Mr. Mazeina said.

The Dubai police have identified 26 suspects in the case, providing an extensive array of evidence that includes passport numbers and photographs, video surveillance, and a narrative of the suspects’ travel to and from Dubai.

Many of the suspects did reconnaissance work for the killing, arriving as early as March 2009, the police here have said. Video surveillance during the final hours before Mr. Mabhouh was killed, late on Jan. 19, show the suspects tracking him to his hotel and even riding the elevator with him to be sure he arrived as expected. Some can be seen disguised in wigs and fake beards, or dressed as tennis-playing tourists.

The case has also become a diplomatic embarrassment for Israel. The names used by at least 15 of the suspects correspond to real people living in Israel and bearing European or Australian passports, whose identities were apparently stolen by the suspects. European officials have called in Israeli diplomats to demand answers, and have opened investigations.

Israel has declined to comment, as is its custom in cases involving accusations against the Mossad.

There is also financial evidence that suggests an Israeli link. The Dubai police have said a company called Payoneer played a role in issuing credit cards for a number of the suspects. Payoneer is based in New York but has offices in Tel Aviv. Its chief executive, Yuval Tal, appeared in 2006 as a commentator on the war between Israel and Hezbollah, identifying himself as a former Israeli special forces soldier.

Mr. Mabhouh played a role in the abduction and killing of two Israeli soldiers in 1989, and was also involved in smuggling weapons into the Gaza Strip, which Hamas has controlled since 2007, Israel and Hamas have said. Israel has said the weapons came from Iran.

Hamas has accused Israel of the assassination and has sworn to retaliate.