Photographs of 11 of the suspects - from the fake British, Irish, French and German passports they used to carry out the killing - have already been released.
The second, as yet unnamed woman, was caught on CCTV camera following al-Mabhouh to his hotel room and identifying him at close quarters, before other members of the team moved in for the kill.
She had arrived at the hotel dressed as a tourist and wearing a large summer hat and was accompanied by a large man in a Panama hat and beard.
Dubai police were last night also questioning two Palestinians, extradited from Jordan, amid allegations they met up with a member of the assassination team before the hit took place on January 20.
Jordanian government spokesman Nabil Sharif said the two had been handed over to the United Arab Emirates several days ago.
Their suspected involvement has led to bitter recriminations between Hamas and the rival Fatah movement, who have been accused of colluding with the Israelis in the attack.
But according to sources in the emirate, the two have a background in the police service in Gaza, suggesting they are more likely to be members of Hamas, which controls the region.
Among the 11 suspects already identified, six were carrying fake UK passports, with details matching those of British citizens living in Israel.
James Clarke, 47, Paul Keeley, 42, Melvyn Mildiner, 31, Stephen Hodes, 37, Jonathan Graham, 31, and Michael Barney, 55, have all expressed their shock after their names appeared on an international wanted list.
Speaking on Wednesday Mr Hodes' wife Gabriella said: "It started like a story that made us laugh, but now we don't know how to take it."
Michael Barney, who lives on a Kibbutz in the western Galilee, added: "This is a mistake or a case of identity theft. I know only that my passport is at home. I don't know who decided to use my name. I'm angry and very surprised."
Mr Clarke, who lives at a Kibbutz called Givat Hashlosha northeast of Tel Aviv, declined to comment except to insist it was not him in the picture.
Mr Graham, Mr Keeley and Mr Mildiner have also insisted they are the innocent victims of an elaborate sting operation.
Irish, German and French passports carried by the other suspects have also been exposed as fakes.
It is believed al-Mabhouh, who is now based in Damascus, Syria, had been travelling through Dubai on his way to Iran to buy weapons for the armed wing of Hamas, of which he was a founding member.
The group has carried out hundreds of attacks and suicide bombings targeting Israelis, and now rules the Gaza Strip.
He was also thought to be involved in the 1989 kidnap and murder of two Israeli soldiers.
According to his brother Hussein, al-Mabhouh had been the target of an assassination attempt on three previous occasions.
Top Hamas figures have denied claims that he was on his way to Iran but have refused to explain why he was in Dubai.