Kolkata, Jan 13 (IANS): Seven persons have been arrested from West Bengal and Jharkhand in connection with the killing of two Trinamool workers, including strongman Srinu Naidu in Kharagpur of West Midnapore district, two days ago, police said on Friday.

"The seven were picked up from places like Ghatal and Jhargram in West Midnapore district, and Jamshedpur in Ranchi," district police superintendent Bharati Ghosh told mediapersons in Midnapore.

Besides killing Srinu and V. Dharma, the assailants lobbed bombs and fired indiscriminately inside the Trinamool party office injuring three other workers on Wednesday.

Srinu Naidu, involved in Mafia activities till some time back, and V. Dharma were pronounced dead in a Kolkata hospital.

The three injured workers were being treated at Midnapore Medical College and Hospital.

"Some old enemies and some others came together to kill him due to old enmity and out of fear that he would emerge in future as a prominent youth leader. The conspiracy was hatched in Bengal and another state," Ghosh said.

She claimed that some big fish were involved in the crime, but refused to categorically state the political connections of the assailants.

"The people we have arrested have confessed to their crimes. They have also mentioned the names of those who pulled the strings and provided logistics to the murderers. You will come to know everything in the near future," said the police superintendent.

She said the police were on the lookout for four others -- two in Bengal and two in another state -- in connection with the twin killings.