POLICE are investigating why an 18-year-old who sparked a cyanide alert may have wanted to take his own life.

Marc Heap, of Swan Farm Close, Lower Darwen, was discovered in the River Darwen at 8.12am yesterday.

Mr Heap's body was taken to Blackburn Infirmary where a post-mortem examination and toxicology tests were carried out.

Officers went to the scene after a letter from Mr Heap, predicting the tragedy, arrived by post at the town centre police station in Railway Road at 7.55am yesterday.

A chemical incident was initially declared and the Environment Agency and Fire Service were alerted because the letter suggested a chemical may have been used.

An Environment Agency spokesman said they were informed cyanide may have been used.

Police have said they were treating the incident as a suspected suicide and there were no suspicious circumstances.

Detective Inspector Giles said: "I have never experienced anything like it. I have never had a body notified by post.

"The letter detailed that a chemical had been used.

"It obviously had to be dealt with with other emergency services and health and safety as paramount.

"There will be toxicology results from the post mortem examination and we will see what that will unearth. It has been a very sad and tragic event."

But DI Giles said he wanted to stress to nearby residents no pollution had been caused by the tragedy.

He said: "The river hasn't been polluted. The police have no concerns regarding the environment or the river.

"Local residents have no reason to worry, there are no issues or concerns for the public."

The man's family were too upset to speak about the death yesterday.