MADISON, Wis. -

A former University of Wisconsin-Madison student pleaded guilty to possessing improvised explosive devices Thursday.

The explosives, which were described as more powerful than TNT, were found inside Andrew Cockerham’s Brooks Street apartment near the UW campus in March.

Madison police said they were alerted to possible explosive materials in the downtown residence by the building’s maintenance and management team, according to the criminal complaint. Police were given pictures showing chemistry-type items including chemicals, a filtration system, beakers, a gas mask and possible fuse material.

The 20-year-old Wauwatosa man told police he is involved in amateur rocketry and chemistry.

Cockerham had lab notebooks with plans that included “very detailed and sophisticated chemistry lab notes on making explosive-type materials,” according to the complaint. He also had erythritol tetranitrate, which is an illegal explosive that is 60 percent more powerful than TNT.

Cockerham told police he created the ETN to make his rocket go faster and farther, according to the complaint. He also said he created it to use in an experiment in which he was hoping to create a heavy body armor piercing round that he would make available to law enforcement if they would ever need it.

University of Wisconsin officials said Cockerham is a former student who studied chemical engineering.