In a decision that stands to save taxpayers money, the state’s highest court ruled Friday that people facing criminal charges carry the burden of proving they cannot afford to pay for their own lawyer before a judge appoints a taxpayer-funded lawyer for them.

The court also said the range of people who may be required to contribute to a person’s legal defense — before taxpayers start paying the bill — can include defendants’ spouses, parents, and even girlfriends and boyfriends.

In three companion rulings, the ­Supreme Judicial Court said defendants are in better position to detail their financial condition than a judge or the state Probation Department, which now handles the task. And, for the first time, the SJC said the burden of proof is on them.

“A criminal defendant is the party in possession of all material facts regarding her own wealth,’’ Justice Francis X. Spina wrote in the ruling involv­ing Diane Porter, the owner of a home care company accused of failing to pay workers. “As such, she should be ­required to bear the risk of failure of proof.’’

In all three rulings, the court said requiring defendants to prove they have limited financial means does not violate their constitutional right, guaranteed by the state and federal constitutions, to a court-
appointed lawyer if they can’t afford to hire one.

A spokeswoman for the state Probation Department, which has primary responsibility for collecting financial data and confirming their accuracy, said officials must first study the ­decisions before they can fully assess their effect.

“An initial review of the SJC rulings on indigency clearly shows that there are significant implications for probation,’’ spokeswoman Coria Holland said in an e-mail. “More time is needed, however, to understand the rulings and their ­impact on this process.’’

Anthony Benedetti, chief counsel for the Committee on Public Counsel Services, which spends about $200 million a year for legal services for the poor in criminal and civil cases, said that the agency rarely handles a case in which a person has a retirement account or bank savings. He said he is concerned that any crackdown on indigency claims will end up affect­ing the wrong people, clients who have little or no money or those who are mentally ill or mentally challenged. He said his agency has been working for the past several years with lawmakers, the Probation Department, and the courts to ­improve accuracy of indigency determinations, but also noted that judges ultimately decide who qualifies, not his agency.

“The overwhelming majority of our clients are indigent, and do not have IRAs, do not have savings,’’ he said.

Benedetti said between private lawyers and public defenders on the state payroll, the agency dealt with 160,000 criminal assignments during the recent fiscal year.

The decision seems likely to save the state money, but it is difficult to assess how much.

According to the office of ­Suzanne Bump, state auditor, a long-term audit of the District Court Probation Department found that often very little ­effort was made to verify defendants’ financial claims.

“Our audit found that millions were being spent on public legal services without the Probation Department collecting or verifying the documentation needed to determine if those services were actually ­deserved,’’ spokesman Christopher Thompson said in e-mail. “Because of the lack of documentation, we are unable to estimate what amount the Commonwealth could have saved. ‘’

Brad B. Bennion, the ­Weymouth lawyer who represented Porter and another ­defendant, said the SJC has rules in place for indigency deter­mination, but those guidelines are not always followed. “In my experience, the rules were always there, but they weren’t applied so strictly,’’ he said. “With the recession that began in 2008, budgets have been tightened . . . and courts are going to start to adhere more strictly to these guidelines to get defendants to pay for their attorney.’’

In the Porter case and in a second case involving alleged drug dealer Joseph Fico, the court also said judges can take into account the finances of spouses and girlfriends and parents, even when the defendant is an adult.

“For, no doubt a variety of reasons, some adult children remain dependent on a parent or parents,’’ Chief Justice ­Roderick Ireland wrote in the Fico decision. “A rational connection exists between the status of a parent supporting a ­dependent adult child and that same parent’s willingness to ­extend that support to pay for legal counsel, in whole or in part, for his or her dependent adult child should the circumstances present.’’

Ireland also wrote that Fico’s girlfriend, who was accused along with Fico, was the couple’s primary breadwinner and as such her income should be included when determining Fico’s financial status. (Ultimately, Fico hired his own lawyer and resolved the criminal charges, according to the SJC.)

Diane Porter and her husband reported a joint income of $60,000 and ownership of three properties. “A spouse has a duty to contribute to the cost of necessaries for the support and maintenance of the other spouse,’’ Spina wrote. “In many cases — including the case at bar, where the alleged crimes involved a business that presumably benefited the defendant’s husband — legal fees will qualify as such ‘necessaries.’ ”

In the third case, which involved Thomas Mortimer IV, who is accused of killing his two children, his wife, and his mother-in-law two years ago in Winchester, the SJC supported a state law, known as “slayer statute,” that bars accused or convicted killers from drawing on financial assets that ­belonged to their victims.

A college fund created for the children Mortimer is ­accused of killing cannot be tapped to pay for his defense, nor could bank accounts that were controlled by the women he allegedly killed, the SJC said.

However, Justice Robert Cordy wrote that some portion of a retirement account that Mortimer controlled is legally available to defray some of the legal expenses taxpayers will bear because the defendant has been assigned court-appointed attorney from the Committee on Public Counsel Services.

“Recognizing the importance of appointed representation, it is critical to conserve the limited resources for those defendants who are truly indigent and unable to fund their legal representation,’’ said Cordy.