Police and FBI agents recovered a package Monday sent by the suspected “Dark Knight” massacre gunman to the University of Colorado medical school that contained writings about killing people, a senior law enforcement official confirmed to NBC News.

Police discovered the package in the mailroom of the University of Colorado Anschutz Medical Campus after being told to look there by the 24-year-old suspected mass killer, James Eagan Holmes, the source told NBC News.

Police recovered the package Monday with Holmes' name in the return address after getting one warrant to search for the package and then a second warrant to open it, NBC News reported. It was unclear how long the package had been in the mailroom.

NBC News' source said the package contained writings about killing people but did not go into any more details.

The development came as the first memorial service for one of the 12 slain victims of the movie theater massacre was being held today.

Gordon W. Cowden, at age 51, was the oldest victim of the tragedy in Colorado last weekend. His two teenage daughters escaped unharmed from the Aurora theater where authorities said Holmes opened fire early Friday during the opening minutes of "The Dark Knight Rises," injuring 58 people.

Cowden was being remembered at Pathways Church in Denver Wednesday ahead of a separate memorial service for the Texas native Friday in Austin, according to reports. Among the 150 mourners who attended Wednesday's funeral were Colorado Gov. John Hickenlooper, Aurora Mayor Steve Hogan and Aurora Police Chief Dan Oates, The Associated Press reported.

"Loving father, outdoorsman and small business owner, Cowden was a true Texas gentleman that loved life and his family," his family said in a statement to Reuters. "A quick-witted world traveler with a keen sense of humor, he will be remembered for his devotion to his children and for always trying his best to do the right thing, no matter the obstacle."

For more on the accused killer's tip to authorities about the package visit NBCNews.com.

Families of other victims have been making arrangements for holding funerals later this week.

John Larimer, a U.S. Navy sailor who was fatally shot after he threw himself onto his girlfriend to shield her, will be remembered at a private funeral and burial in Texas. A public visitation is set for Friday at Davenport Funeral Home in the Dallas suburb, NBC DFW reported.

Jessica Ghawi, the 24-year-old aspiring sportscaster who was the first shooting victim to be identified, will be remembered at a memorial service in San Antonio on Saturday at the Community Bible Church, her brother wrote on his blog.



Meanwhile, Batman actor Christian Bale met with several shooting survivors, first responders, police and Colorado Gov. John Hickenlooper in Aurora on Tuesday.

Twenty people remained hospitalized Tuesday, seven of them in critical condition and two in serious condition, Reuters reported.

More details have emerged about Holmes and the booby-trapped apartment authorities said he left behind.

Holmes was one of six graduate students admitted to the University of Colorado’s graduate program in neuroscience last year, and had been awarded a $26,000 federal grant before he began the process of withdrawing from the school, USA Today reported.

The former doctoral student allegedly filled his Aurora apartment with 30 homemade grenades fashioned from plastic fireworks shells and gunpowder — alongside glass jars filled with gasoline and gunpowder and another 10 gallons of gasoline, a police source told the Denver Post.

The deadly cocktail of explosives was mostly concentrated in Holmes’ living room, and could have set the entire building ablaze, the source told the Post.

After authorities disabled a control box attached to a trip wire Saturday, the explosives were carted away in a sand-filled dump truck and detonated in a remote location, according to the paper.

Holmes is expected to be formally charged Monday as the sole suspect in the deadly theater rampage in Aurora early Friday. Holmes, who had dyed his hair red and orange before the massacre, told police who apprehended him afterward that he was the Joker, one of the supervillains from the Batman saga, according to authorities.

At his first court appearance Monday for an advisement hearing, Holmes’ hair was still dyed red and orange. He slumped in a jury box, showed no emotion and rarely made eye contact, raising speculation about his mental state.

Authorities said Holmes set off gas canisters in the early minutes of the new Batman film, then sprayed the room with bullets while dressed all in black and outfitted in body armor and a gas mask. Witnesses said that at first they mistook the gunman for a planned part of the show — but then "mass chaos" broke out.

Amid the terror, there emerged stories of heroism, thanks to theatergoers who sacrificed themselves to protect their loved ones.