CHICAGO (AP) — The former Iowa letter carrier accused of sending letters and dud pipe bombs to investment advisers on Wednesday presented his defense, while at the same time admitting to some of the charges.

John Tomkins, who is serving as his own defense lawyer, made his opening statement and called three character witnesses, two of them his brothers.

Tomkins told the federal jury in Chicago he will ask them to find him guilty of mailing threatening letters to investment houses, but not guilty of mailing pipe bombs that were ready to explode, which he said he did not do.

'He mailed threatening letters,' said Tomkins, referring to himself in the third person. 'Hold him accountable for what he did.'

Tomkins is charged with mailing threatening communications, illegal possession of a destructive device and using a destructive device in connection with a crime of violence.

The government alleges Tomkins wanted investment houses to raise the price of stock he owned in two technology firms.

'He did not construct destructive devices,' Tomkins told the jurors. 'Don't punish him for what he didn't do.'

Prosecutors allege Tomkins sent letters from 2005 until 2007 that threatened to kill those who received them, their families and neighbors unless they took action to raise the stock prices of 3COM Corp. and Navarre Corp., in which Tomkins had invested. They allege he mailed the pipe bombs from a suburban Chicago post office in 2007.

Tomkins, who Assistant U.S. Attorney Patrick Pope said identified himself in some of the letters as 'The Bishop,' allegedly taunted the people who received them.

'Bang, you're dead,' Pope quoted from one of the letters that accompanied a pipe bomb during his opening argument. 'The only reason you're alive is that I did not attach one wire.'

Prosecutors said the pipe bombs were real and would have detonated had all the wires been attached. Pope said the letters included a threat that the advisers better drive up the stock prices by a deadline he gave them or he would send more bombs, making sure to 'connect all the wires,' before ending with the words 'Tick, tock' or 'Time's up.'