Police arrested a 29-year-old youth on Monday, who allegedly posted all the six letter bombs to different addressees in Thiruvananthapuram recently.
Rajeev, an electronics diploma-holder hailing from Kazhakootam, has confessed to his crime, Director General of Police Raman Srivastava told reporters.
"The motive behind the crime was personal enmity. He had differences with the persons to whom the letters were sent," Srivastava said.
Prima facie evidence against the youth have been gathered during his questioning, police said.
ADGP (Intelligence) Jacob Punnoose, who was also present, said the role of some others in the crime could not be ruled out, adding that the investigation would continue.
"The accused does not appear to be motivated to kill anyone. He wanted to create a scare since only explosives in small quantities was packed in the letters. He tried to increase the blast's impact by also sending threatening letters," IG(south zone), Arun Kumar Sinha, who led the probe team, said.
Srivastava said so far no terrorist or political angle to the two blasts that occured on September 21 were revealed.
Two letter bombs exploded last month, one in a post office and other in a nearby local area, while the other four postal bombs detected later in the city post offices were diffused by the police.
