The bomber, believed to be a man aged between 20 and 25 who was not from Lebanon, detonated explosives weighing about 1,800kg (3,960lb) in a minivan and died in the blast that killed 22 other people, according to a UN report.
"The commission has identified a considerable number of new leads for investigation relating to the crime scene, its vicinity and the immediate perpetration of the crime," the report said.
Investigators said they had found 32 pieces of remains from the man believed to have bombed al-Hariri's convoy as it wound through Beirut in February last year.
Evidence found at the scene of the blast also included a tooth, probably of the bomber, which featured an unspecified "distinguishing mark" on its crown suggesting that he may not have been from Lebanon, the report said.
Investigators said Syria had been generally co-operative with the investigation.
John Bolton, the US ambassador to the UN, said that it looked as though Serge Brammertz, a senior Belgian judge heading the investigation, appeared to be nearly ready to present the case in court.
"He is getting closer and closer to trial, closer and closer to a point where he is ready for a trial," Bolton said.
Brammertz's predecessor as chief of the investigation, Detlev Mehlis, a German, had said the killing's complexity suggested that the Syrian and Lebanese intelligence services played a role in al-Hariri's assassination.
In one report, Mehlis had implicated Brigadier-General Assaf Shawkat, Syria's military intelligence chief and the brother-in-law of Bashar al-Assad, the Syrian president.
Brammertz said evidence suggested that the team planning al-Hariri's assassination had him under surveillance.
At one point, the attackers either tried to kill al-Hariri or carried out a rehearsal.
Al-Hariri was a quiet opponent to Syria's 30-year dominance of Lebanon.
His killing provoked an international outcry and led to Syria withdrawing thousands of troops from Lebanon in April 2005.
Al-Hariri's supporters blamed the attack on Syria, which has denied any role.