W ASHINGTON—U.S. District Judge Amit Mehta heard two days of closing arguments last week in the government’s landmark antitrust case against Google. Mehta lobbed skeptical questions toward lawyers for both sides, along the way dropping hints about how he’ll rule when he hands down his long-awaited written decision.

Whenever you type a search into Apple’s Safari browser — say, on an iPhone — chances are it’s Google that returns the results.

Google's preeminence as an internet search engine is an illegal monopoly propped up by more than $20 billion spent each year by the tech giant to lock out competition, Justice Department lawyers argued Friday at the closing of a high-stakes antitrust lawsuit.