The detectives 'dug into' his past and learned that he had once lived in another country.
Her fingernails 'dug into' my hand. = She 'dug' her fingernails 'into' my hand.
The salesman 'dug in his heels' and refused to lower the price any further.
(..) been a big morale boost here for our teams to have met you had you actually been Dr. Cassandra Railly. You do look like her. It was his false ID that tipped us off. We dug a little deeper. It turns out Dr. Railly was confirmed dead at the CDC by our own personnel... so you can't be her. (..)2016 TvShow: 12 Monkeys Title: Lullaby Season: 2 Episode 8