New Delhi: A day after more than 40 Delhi schools received a hoax bomb threat e-mail, police on Tuesday registered an FIR and wrote to Google, seeking the IP address of the sender, official sources said.

At least 44 schools in the national capital received a bomb threat mail on Monday morning with the sender demanding USD 30,000. After a thorough search, the call was announced to be a hoax by police.

The New Delhi Range of the Special Cell -- the anti-terror unit of the Delhi Police -- registered the first information report and is probing the case, an official said.

"The Delhi police has written to Google to ascertain the IP address of the sender who sent the threat mail from a Gmail ID," the source said.

Police, however, believe the sender might have used a virtual private network (VPN) to mask his/her identity, the source added.

The threat was sent in a single e-mail marked to all the schools at 11.38 pm on Sunday from scottielanza@gmail.com.

It read, "I planted multiple bombs inside the building. The bombs are small and hidden very well. It will not cause very much damage to the building, but many people will be injured when the bombs detonate."

"You all deserve to suffer and lose limbs. If I do not receive $30,000. The group =E2=80=9CKNR=E2=80=9D is behind this attack (sic)," it said.

In May, more than 200 schools, hospitals and important government installations in the city received a similar threat. The case is yet to be solved as the mail was sent using a VPN.

Police had also taken the help of central agencies to get the IP address of the sender back then.