They also suspect the involvement of a Jemaah Islamiyah (JI) splinter group.
The release of the pictures comes after an Indonesian news channel aired footage of a man thought to be one of two suicide bombers.
Police said the sketches are based on two heads found at the bomb sites.
"From the two heads in the bomb sites we believe these were the human bombs or suicide bombers," Nanan Soekarna, said a police spokesman at a news conference.
One shows a chubby-faced, dark-skinned man, who police said was aged between 20 and 40 years and, standing at around 165cm in height, with short, straight black hair.
His remains were found at the Ritz-Carlton.
The second suspect, found at the Marriott, had a thinner, oval-shaped face, and was lighter-skinned with sunken eyes, and short, straight black hair.
Police said he was between 20 and 25 years and about 180cm tall.
Police also said the bombers checked into the Marriott as paying guests on July 15 and assembled the bombs in their room, 1808 on the 18th floor.Planned operation
A third bomb was found and defused in a laptop computer bag in room 1808.
A police source told Reuters news agency on Monday that one theory they are working on is that the bombers planned to detonate the bomb on the 18th floor first,
sending panicking guests rushing down to the lobby where one of the suicide bombers would detonate a second bomb, potentially killing and injuring many more guests.
The bombings last week ended a four-year lull in violence and, according to police and security analysts, carried the hallmarks of JI, in particular of a breakaway faction led by key member, Noordin Md Top.
Noordin, a fugitive Malaysian bomb-maker, has been blamed for previous attacks on foreigners and Western targets including bars and hotels.