An Islamist group calling itself Agnad Misr, or Soldiers of Egypt, has claimed responsibility for the blasts that killed a senior police officer at Cairo University on Wednesday.
In a statement issued on Wednesday, the group said it was targeting police "criminals" guilty of "massacres" – an apparent reference to the government's crackdown on Islamists following the overthrow of president Mohamed Morsi last summer.
A senior police officer was killed and five other policemen wounded when twin bombs went off near the university in central Cairo on Wednesday morning.
A third bomb struck near the university's main gates almost two hours later, with no casualties reported.
Agnad Misr said the third explosion was delayed to avoid harming civilians who had gathered at the scene.
The group had claimed responsibility for a number of small-scale bomb attacks in Giza and Cairo in recent months.
It said Wednesday's bombings were in retaliation for the detention of Islamist women, and vowed to continue its campaign until they are released.
Hundreds of Islamists have been killed and thousands detained in a clampdown since Morsi's removal
Wednesday's blasts were the latest in a series of attacks against police and members of the security forces.
According to a government tally, almost 500 people, mostly policemen and troops, have been killed in suicide attacks, bombings, and shootings since Morsi's ouster.