Dhahi Khalfan, the Dubai police chief, renewed his accusation that the Israeli spy agency Mossad was responsible for carrying out the crime.
He called on Meir Dagan, who head's Mossad, to step forward and accept responsibility.
"Dagan, the boss, should admit the crime ... or present a categorical denial," the government daily Emarat Al-Youm quoted Khalfan as saying.
"But [Dagan's] current attitude shows he is afraid. Let him be a man, and tell the truth," Khalfan said.
Israel has neither confirmed nor denied any role in the murder, though it knew al-Mabhouh played a role in securing arms for the Palestinian authority in Gaza.
Succinylcholine, also known as suxamethonium, is used to induce muscle relaxation and is favoured by anaesthetists and emergency doctors because it quickly takes effect.
Al-Mabhouh, one of the founders of Hamas' military wing, was found dead in his hotel room on January 20.