ROCKVILLE, Conn. — Connecticut’s top prosecutor testified Wednesday that the state had no written policies on when to seek the death penalty but that state law provided enough guidance.

Chief State’s Attorney Kevin Kane was the first witness to testify in a trial involving five death row inmates who charge that prosecutors’ decision-making process in death penalty cases has been arbitrary and fraught with racial and geographical biases. The inmates are suing the state, seeking to have their death sentences overturned.

Connecticut repealed the death penalty this year, but ­only for future capital crimes. There are 11 inmates on the state’s death row.

Lawyers for the inmates asked Kane about how he decided to seek the death penalty when he prosecuted cases in the New London Judicial District from 1986 to 2006. State’s attorneys in Connecticut’s 13 judicial districts are independent officials responsible for all criminal cases in their regions, while the chief state’s attorney is essentially an administrative position.

Attorneys Richard Reeve and David Golub suggested in their questioning that the state’s attorneys used different processes for determining when to seek the death penalty, which they say created an arbitrary system.

The inmates charge that prosecutors’ decision-making process has been arbitrary and fraught with racial and geographical biases.

‘‘The state’s attorneys have the obligation to find out if they’re using the same criteria,’’ Golub told Judge Samuel Sferrazza. ‘‘Otherwise you have a standardless system.’’

Kane said he did speak informally with prosecutors in other districts about death penalty cases. He acknowledged there were no written state policies on when to seek the death penalty, but said state law provided guidance.

‘‘I believe the same guidelines were followed by everybody,’’ Kane said.

Kane said there were death penalty-eligible cases in which he decided to reduce the charges because of a variety of factors, including the strength of the state’s case and the presence of mitigating factors for the defendant.

‘‘I believe I had discretion to do that,’’ Kane said about deciding to not pursue the death penalty in some capital cases.

All 13 state’s attorneys and some former prosecutors were expected to testify at the trial. But inmates’ lawyers and government attorneys reached a deal Wednesday that will spare 25 witnesses from testifying, including the state’s attorneys.

The trial was recessed until Tuesday because of the agreement, in which prosecutors agreed that the state had no written policies or standards on when to seek the death penalty or when to reduce capital charges to lesser crimes.

Prosecutors also agreed to stipulate that there were no formal discussions among prosecutors statewide about criteria for seeking the death penalty and that each state’s attorney in each judicial district made decisions in death penalty cases based on criteria they thought were appropriate.

The trial is being held in a prisoners’ common room at Northern Correctional Institution in Somers, while the media watched a video feed in a courtroom in Rockville Superior Court about 15 miles away.

The death row inmates wore yellow prison suits Wednesday and sat handcuffed in white plastic chairs at tables. Some sat with their lawyers and some did not. In front of the inmates is a row of tables for prosecutors and inmates’ lawyers, and in front of that is another row of tables for the judge, judicial staff, and witnesses.

The trial is expected to run for about another week.

The key evidence for the inmates is a study by Stanford University professor John Donahue, who reviewed the nearly 4,700 homicides in Connecticut from 1973 to 2007.

Donahue said he found that minority defendants who killed white victims were three times as likely to receive a death sentence as white defendants who killed white victims. He also found that minority defendants who commit death penalty-eligible slayings of white victims are six times as likely to receive a death sentence as minority defendants who commit death penalty-eligible homicides of minority victims.

The study, commissioned by the chief public defender’s office, also concluded that Connecticut’s capital punishment system included geographic biases. Donahue is expected to testify next week.

State prosecutors disagree with the study’s findings. They hired their own expert who reviewed death penalty cases and disputed the Donahue report.