When the bodies were found early Thursday, the office was locked from the outside. Three bullet casings were found on the floor. Blood was splattered on the door.

One of the dead women was a founder of the Kurdistan Workers’ Party — or P.K.K. — a Kurdish separatist group that has waged a guerrilla war against Turkey since 1984. The other two were Kurdish activists who may well have died because they were simply in the wrong place at the wrong time.

There were competing theories over who was responsible, and outraged Kurds poured into the street in Paris, blaming Turkey. Officials there said the killings were probably a dispute among Kurds, perhaps intended to derail new peace talksbetween the government and the separatist group’s jailed leader, or to settle a score.

But these were theories. The evidence spoke only to a well-planned job.

“No hypothesis can be excluded at this stage” about the motive, said Agnès Thibault-Lecuivre, a spokeswoman for the Paris prosecutor’s office. Visiting the crime scene on Thursday, Interior Minister Manuel Valls called the killings “intolerable” and said they were “without doubt an execution.”

The shootings took place in the gritty 10th Arrondissement of the city, near the Gare du Nord railroad station, in a working-class immigrant neighborhood of Turkish kebab shops and African hair salons. The killings prompted outrage, raised fears of violent revenge and opened a new chapter in the often murky annals of Kurdish exile life.

The bodies were found around 2 a.m. inside the Kurdish Information Center on Rue La Fayette, which is used to promote Kurds’ political and cultural agendas. Someone would have to have known the office was there — there was no plaque outside. And the front door could be opened only with a digital code or if the occupants buzzed someone in, the manager of the center, Leon Edart, told reporters.

That possibility led to many questions. Did the women know their killer? Did the killer slip into the center behind a welcomed guest? An organization called the Federation of Kurdish Associations in France, representing many of the estimated 150,000 Kurdish exiles in the country, added to the intrigue, saying in a statement that the victims might have been killed with weapons equipped with silencers.

“Why anyone would want to do this is unclear,” said Rusen Werdi, a lawyer at the Paris Kurdish Institute, which is near the information center on Rue La Fayette, and who knew two of the women. “It was an ambush.”

The bodies, she said, were discovered after friends became concerned about the women because cellphone calls had gone unanswered and none of them had returned home.

Ms. Thibault-Lecuivre said the antiterrorism department of the prosecutor’s office would oversee the investigation.

The authorities confirmed the identities of two of the victims: Leyla Soylemez, a young Kurdish activist, and Fidan Dogan, the head of the Kurdish Information Center and a representative of the Kurdistan National Congress. News media reports said the third woman was Sakine Cansiz, a founder of the Kurdistan Workers’ Party.

But for all the mystery, Ms. Werdi said, it appeared that the target was Ms. Cansiz and that the other two victims might well have been killed because they were with her.

Ms. Werdi said that at least one of the women, Ms. Cansiz, had been under surveillance by the French police because of her activism. She said that Ms. Cansiz had been keeping a low profile in recent months, and that it was rare for her to be at the information center.

The Kurdish separatist group is no stranger to infighting and internal strife. Hurriyet, a Turkish daily newspaper, said Ms. Cansiz was “known for her opposition to the alleged head of the P.K.K.’s armed wing, Syrian citizen Ferman Hussein.” But Kurdish activists said she was very close to Abdullah Ocalan, the head of the P.K.K., who has been in prison since 1999 in Turkey.

Ms. Cansiz had been in Paris since 2007, after the authorities in Germany arrested and briefly held her before rejecting Turkey’s request for her extradition. She also was imprisoned in Turkey in 1979 and freed in 1991 for her activism, after which she became involved in the separatist group, fellow activists said. She played a leading role in garnering financial and political support for the Kurdish cause in Europe.

Dorothée Schmid, an expert on Turkey at the French Institute of International Relations in Paris, did not rule out the possibility that the killings could have been the work of extreme Turkish nationalists, some of whom are virulently opposed to negotiations that would lead to Turkey’s granting Kurds further rights and autonomy. Turkish analysts and officials have long talked of a “deep state” in Turkey, a group of operatives, linked to the military, who are thought to have battled their perceived enemies since the end of the cold war.

The P.K.K. has been fighting the Turkish authorities for almost three decades to demand greater autonomy. The conflict, in which an estimated 40,000 people have been killed, is fueled by competing notions of national identity that are rooted in the founding of modern Turkey on the ruins of the Ottoman Empire by Mustafa Kemal Ataturk in 1923. Kurds account for about 15 million of Turkey’s 74 million people.

Turkey, the United States and the European Union have labeled the group a terrorist organization, but sympathy for it and its goals remains widespread in many towns in Turkey’s rugged southeast.

Huseyin Celik, the deputy chairman of the governing party in Turkey, the Justice and Development Party said: “Whenever in Turkey we reach the stage of saying, ‘Friend, give up this business, let the weapons be silent,’ whenever a determination emerges on this, such incidents happen. Is there one P.K.K.? I’m not sure of that.”

Restive Kurdish minorities live in a broad region that includes Turkey, Syria, Iraq, Iran and parts of the former Soviet Union. Regional turmoil in recent years has emboldened Kurdish separatists, inspired by the example of Iraqi Kurds who control an autonomous zone. Turkey fears that the civil war in neighboring Syria may strengthen the separatist yearnings of Kurds there.

In recent years, Turkey has sought to clamp down on Kurdish activists outside of the country, including in France, Germany, Belgium and Denmark, where Kurds have established sizable communities as well as civic groups and media outlets that Kurdish officials say are a refuge from Turkish censorship. Turkey has accused some of the groups of being fronts for separatists or terrorists.

In Paris, the mood was angry and somber as hundreds of Kurds filled the street outside the building where the bodies were found. Some people waved Kurdish flags while others chanted, “We are all P.K.K.!” On Thursday evening a single police officer stood guard outside the information center’s office. Six roses, five red and one white, were laid against the door.

Scott Sayare contributed reporting from Paris, and Sebnem Arsu from Istanbul.