Charred bits of plastic that fell from the sky after the Oklahoma City bombing (search) are chemically similar to plastic barrels found at the home of Terry Nichols (search), a federal investigator testified Monday at Nichols' murder trial.

Four of the 55-gallon barrels sat within arms' length of Nichols' jury as FBI agent Richard Buechele, who worked at the agency's crime lab in Washington when the bombing of the federal building occurred, testified about their chemical composition.

Buechele said the plastic shards and the barrels found at Nichols' Kansas home days afterward were both high-density polyethylene plastic.

FBI agent Gregory Carl said investigators found the small pieces of plastic in debris on top of the Journal Record Building, located across a parking lot from the federal building, four days after the bombing.

The April 19, 1995, bombing killed 168 people. The convicted mastermind, Timothy McVeigh (search), was executed in 2001.

Nichols, 49, was convicted in 1997 on federal charges in the bombing and was sentenced to life in prison. He is now on trial in Oklahoma state court on murder charges that could bring the death penalty.

Nichols' attorneys are expected to put the FBI crime lab itself on trial and argue that the forensic testimony in unreliable because of laboratory contamination and mishandling of evidence.