"Mumbai police shared some information on the basis of which Shiv Kumar alias Sadhu Rajbhar, a resident of Badagaon, Varanasi, has been detained by UP STF," IG (law and order) A Satish Ganesh told reporters here.
He said documents related to the victims were recovered from the possession of Shiv Kumar who has been taken into custody.
"He will be handed over to Mumbai police team which has already arrived here. The Mumbai police will probably produce him in court tomorrow," the IG said.
Police are also ascertaining whether Kumar was the last person to call Hema.
Three suspects were yesterday detained in Mumbai in connection with the case.
The bodies of Hema and her lawyer Harish Bhambhani were found packed inside cardboard boxes lying near a drain in suburban Mumbai on Saturday.