Criminal defendants in Massachusetts must prove that they can’t afford their own attorney before a judge can appoint a lawyer to represent them at taxpayer expense, the state’s highest court ruled Friday.

In a series of rulings, the Supreme Judicial Court tightened rules governing when defendants can get court-appointed lawyers.

The SJC also found that retirement account funds can be considered when calculating whether a defendant is indigent, ruling in the case of a Winchester man accused of killing his wife, two young children and mother-in-law in 2010. The court rejected Thomas Mortimer IV’s claim that his retirement account cannot be used to help pay for his defense.

Mortimer’s lawyer had argued that the money in his IRA account cannot be considered liquid assets and should not be counted when determining his indigency or ability to contribute to the cost of his defense.

The SJC, however, said the money could be used, excluding any early withdrawal penalties and taxes.