Last month, Rashied Mitchell shot and killed a Seattle mother, Tabitha Apling, in front of their two young children. At the time, Mitchell was subject to a court order barring contact with Apling, his ex-girlfriend. Mitchell had a rap sheet of at least 12 prior similar convictions, and had been arrested for an alleged domestic violence attack against Aplin just days before her death.

This scenario is not unusual. Under federal law, anyone convicted of domestic violence or subject to a domestic violence protective order is prohibited from possessing a gun. But abusers are often able to buy a firearm anyway, or are allowed to keep one they already own, and they end up using it to shoot a wife, girlfriend, or other intimate partner.

So how is it that known abusers, convicted of a crime or subject to a restraining order, come to have a firearm in their possession? Often, they are able to exploit gaps in the federal background check system or in state laws designed to remove firearms from abusers’ homes. Here are seven ways that commonly happens.