Try crime mapping sources, there are several, so you can check different ones if the area you're looking into is not covered by the first one. You can just enter the address or city name and look up incidents by block and street
DC Goverment public documents unit provides arrest and police reports. Following the link https://mpdc.dc.gov/service/police-reports there's a link on the left column which will go directly to the type of police report you need to request. Requests can be made by mail or in person. There's a fee waiver for complainants, their spouse or parent/guardian of a minor. Walk-in location for these requests is 300 Indiana Avenue NW, Room 3075, Washington, DC 20001.
Restrictions on high capacity magazines and background checks do not have much to do with each other. If a ban is in place, regardless of whether an individual passes the check or not, they will not be able to obtain them as per law.
These laws are federal, states such as California have these rules already in place, such as the ban on high capacity magazines.