Dubai, United Arab Emirates (CNN) -- Another person has been added to the list of suspects in the January killing of a Hamas leader in a Dubai hotel, bringing the number of identified suspects to 27, two sources told CNN on Monday.
Twenty-six of the 27 were carrying European and Australian passports, authorities have said. The sources, an official familiar with the investigation and a police source, did not say which nation issued the passport the suspect used.
Mahmoud al-Mabhouh, a founding member of Hamas' military wing, was found dead January 20 in his Dubai hotel room. Police believe he was slain the night before, allegedly by the secretive Israeli foreign intelligence unit Mossad.
Earlier Monday, sources in Dubai said two of the suspects ultimately entered the United States after al-Mabhouh's death, confirming a story originally reported by the Wall Street Journal. But a national security source in the United States cast doubt on that report.
Federal authorities ran the two names -- Roy Allen Cannon and Evan Dennings -- through databases and found no indication that anyone with those names or using those names entered the United States after the Dubai killing, the U.S. source said.
The Dubai sources said the suspect identified as Dennings, carrying an Irish passport, went to Zurich, Switzerland, immediately after the slaying, then entered the United States on January 21. The suspect identified as Cannon entered the United States on a British passport on February 14, the sources said.
Both should have been required to provide fingerprints and a picture upon arrival in America, the sources said.
On Sunday, Dubai's police chief said he is "100 percent sure" that the secretive Israeli foreign intelligence unit Mossad is behind al-Mabhouh's death.
"The Mossad needs to be ashamed of its actions," said Lt. Gen. Dahi Khalfan Tamim. "They sent 26, 27 persons to assassinate one man who was involved in the capturing and killing of two Israeli soldiers."
Hamas has said al-Mabhouh was behind the 1989 deaths.
Israel has a stated policy on security matters of neither confirming nor denying involvement. Foreign Minister Avigdor Lieberman, however, told Israel Army Radio earlier this month, "There is certainly no reason to think that the Mossad and not some other intelligence agency of another country operated there."
Lieberman has also said only "media reports" link Israel to the slaying.
Asked about the case Saturday by CNN's Christiane Amanpour, Israeli Defense Minister Ehud Barak repeatedly declined to comment.
Earlier Sunday, police said toxicology results showed that al-Mabhouh was injected with succinylcholine, a drug used to relax muscles during surgery or as an anesthetic, before he was suffocated. Signs indicated that al-Mabhouh resisted as he was being suffocated, police said.
Family members were told earlier that police had found blood on a pillow. Authorities have also said the killers left some of al-Mabhouh's medication next to him in an apparent effort to make the death appear natural.
But "the medication left next to him in the room has nothing to do with the killing," Tamim said Sunday.
However, authorities have recovered evidence including DNA, he said. "The DNA evidence is quite important and will help us with the investigation."
The 27 suspects are believed to have acquired false passports to travel to Dubai for the killing, then scattered to several far-flung locations afterward.
Tamim said Sunday not all the suspects have fraudulent passports -- "We know some of the names are real."
The total of 27 does not include two Palestinians previously arrested in Jordan and returned to Dubai. Tamim said one is not believed to be directly involved in al-Mabhouh's death, but "he is wanted by one of the Palestinian factions in the Palestinian territories and he is sentenced to death and that's why we will extradite him." He declined to discuss anything about the other Palestinian.
Twelve of the suspects used British passports, police said. Six suspects used Irish passports, four used French passports, three used Australian and one used a German passport.
Also Monday, the sources said the UAE central bank is working with other nations to track funding and 14 credit cards -- issued mostly by a United States bank -- used by the suspects in different places, including the United States.
CNN's Caroline Faraj and Saad Abedine contributed to this report.