Colorado shooter James Holmes was able to acquire large amounts of ammunition and rapid-fire weaponry despite his erratic behavior. (AP Photo/Denver Post, RJ Sangosti, Pool.)

If the mass shooting this summer during a midnight screening of The Dark Knight Rises has receded in the public’s memory given the recent horror in Newtown, Connecticut, court proceedings in Centennial, Colorado, this week have thrust it back into view.

We’ve learned heretofore unknown and certainly unpleasant details from the day of the shooting. Prosecutors played a tape in which a panicked moviegoer calls 911, but the dispatcher can’t hear him over the sound of gunshots—30 of them in 27 seconds. An officer testified that, when there weren’t enough ambulances around, he crammed victims into the back of his patrol car. They were so badly injured that he testified he could hear blood “sloshing around” on the floor of his car when he made turns.

Other details that we heard piecemeal before have been confirmed: about the types of weapons Holmes used and his efforts to obtain them.

Crucially, looking at the evidence presented by prosecutors this week, it’s easy to see several points at which sensible gun control legislation could have stopped the slaughter. Here are the three most obvious ones:

Tracking large-scale ammunition purchases. Steve Beggs, an agent for the Bureau of Alcohol, Tobacco, and Firearms, testified that Holmes went on a buying spree starting May 10, 2012. By July 14, he had bought 6,300 rounds of ammunition, two pistols, a .223 caliber Smith & Wesson AR-15 assault weapon, a shotgun, body armor, bomb-making materials and handcuffs.

The large-scale bullet purchases are the big red flag here. Nobody is monitoring bulk ammunition purchases: Some states, like Illinois, Massachusetts and New Jersey, have limits on the amount you can buy and ask that dealers track their sales for law enforcement, but Colorado has no such rules. And the ones that do exist can easily be evaded by buying ammunition online anyhow, which is what Holmes did.

The federal government should be able to track bulk ammunition sales—there is clearly a controlling public interest when somebody is assembling an arsenal that could support a small militia. If authorities had even briefly question Holmes about why he was stockpiling so many weapons, it’s almost a certainty they would have noticed his extremely bizarre behavior: He was reportedly almost incoherent in the weeks leading up to the attack. The White House is said to be considering a national database to track the sale and movement of weapons, and it should absolutely include ammunition, too.

Online sales of ammunition should also be banned or highly regulated, since they create an easy way for people to stockpile dangerous weapons without ever showing their face. A 1999 bill in Congress to regulate the online sale of ammunition was never adopted, but should be now. 

Better mental health screenings for weapons purchases. Holmes was not only stockpiling weapons but, as noted, exhibiting excessively strange behavior. He left a voicemail at a local gun range asking if he could join, but the message was reportedly incomprehensible. “It was this very guttural, very heavy bass, deep voice that was rambling incoherently,” the owner of the range told The New York Times. “It was bizarre on a good day, freakish on others.” Only weeks before his rampage, Holmes’ psychiatrist was alerting police at his university about his behavior—a drastic step for any mental health professional to take.

Yet, Holmes was able to obtain his weapons with ease. Note this exchange during yesterday’s court proceedings:

Holmes’ defense attorney Tamara Brady asked [ATF agent] Beggs if there is a legal process to keep from selling these items legally in Colorado to a “severely mentally ill person.” Beggs answered that there is not.

Biden’s task force on gun control has reportedly been exploring the idea of mandating state participation in the mental-health database and stronger mental-health screenings for gun purchasers—areas in which it might find common ground with the NRA. Those measures should certainly be part of the final package.

Banning assault weapons and large capacity magazines. Holmes used a .223 caliber assault rifle during the attack, which as noted was heard firing 30 shots in 27 seconds. Holmes also bought ammunition drums larger than the standard 30-round high-capacity clip, including one that held up to 100 rounds.

According to details disclosed in court, at most 90 seconds elapsed between the first 911 call and police intervention in the movie theatre, yet Holmes was able to shoot 71 people. Many gun-control advocates rightly find this to be an unacceptable level of firepower, and Biden’s group will almost certainly propose an assault weapons ban and high-capacity clips. In the Senate, Dianne Feinstein is moving towards strong legislation that would do the same.

What’s important is that, unlike the 1994 ban, the new laws should make all assault weapons illegal—the language should be strong enough that gun manufacturers can’t evade the ban with minor alterations to their weapons. Feinstein’s bill would make only one military characteristic illegal, whereas the 1994 ban had the threshold at two.

Why has gun ownership come to center on self-protection with high-powered weapons? Rick Perlstein looks at the NRA and the rise of vigilante culture in the United States.