He left no DNA in any criminal database because he was not convicted of any crime that required DNA submission. His one known arrest — the 1979 shoplifting — did not result in a conviction that triggered DNA collection requirements, which in any case did not exist in their current form in 1979.
He did not talk about the crimes. There is no record of him having told anyone what he had done. Some serial offenders communicate about their crimes, either through taunting of investigators or through personal boasting that eventually reaches the investigative record. DeAngelo apparently did not communicate in ways that reached outside his own knowledge.
He lived in the Sacramento area — the same area where the EAR crimes had occurred — without triggering reinvestigation based on his location or behavior. Investigators over the years developed profiles that pointed toward someone with a law enforcement background, and that profile applied to a large population of people who had nothing to do with the crimes. The profile was accurate but not specific enough to be actionable without other corroborating evidence.
The crimes themselves stopped after 1986. Whether this was a deliberate choice, a response to life circumstances, or a change in whatever motivated the crimes is not established in the investigative record. DeAngelo had a family — children were born in the 1970s and 1980s — and it is possible that family life created constraints on the kind of nocturnal activity the crimes required. But this is inference, not documented fact, and the case record does not provide a reliable account of his inner life or decision-making.