How did cities solve the problems of crime and fire?

Cities developed professional firefighting and police forces.

Each person has their own DNA profile, unless they are identical twins, in which case they would have the same profile, but unique fingerprints. Forensic scientists can use the DNA profile of a suspect and compare it to a profile that they found at the crime scene. Any DNA profiles that are on record, the same way fingerprints can be on record, is kept in CODIS (Combined DNA Index System). This is one way of positively identifying a person.