In celebrating WNBA star Brittney Griner's release, President Joe Biden made a point on Thursday to say the prisoner swap was "not a choice" between Griner and Paul Whelan, the American former Marine who is still detained in Russia.
"We never forgot about Brittney. We've not forgotten about Paul Whelan, who has been unjustly detained in Russia for years. This was not a choice of which American to bring home," Biden said from the White House. "Sadly, or totally illegitimate reasons, Russia is treating Paul's case differently than Brittney's, and while we have not yet succeeded in securing Paul's release we are not giving up. We will never give up."
Elizabeth Whelan, Paul's sister, on a Zoom interview from Massachusetts in the afternoon, told ABC News the family had expected Griner might return first.
"We've always known that the Russians were treating Paul separately, and therefore, we always knew that there was a chance that this would happen, that would Brittney would be released first," she said.
"We're upset. We want Paul home," she added. "We're angry at Russia for for playing him around like this, for playing all of us around like this, but what we need to do is look forward to the plan to get him home."
Whelan has spent four years in detention since he was seized in 2018 by Russia's domestic intelligence agency, the Federal Security Service, while visiting Moscow for a friend's wedding. He was sentenced to 16 years in prison on espionage charges but the United States and his family say they were fabricated in order to take him as a political bargaining chip.
In a phone interview with CNN on Thursday, Whelan said he was "greatly disappointed" to not also be returning home.
"I have to say I am greatly disappointed that more has not been done to secure my release. Especially as the four-year anniversary of my arrest is coming up. I was arrested for a crime that never occurred," Whelan said. "I'm happy that Brittney is going home today and that Trevor went home when he did -- but I don't understand why I'm still sitting here," he added.
He said he hopes officials will do everything they can to bring him home, "regardless of the price they may have to pay at this point."
"My bags are packed. I'm ready to go home. I just need an airplane to come and get me," Whelan said.
Some Republicans on Capitol Hill were quick to blast the prisoner swap, including House Republican Leader Kevin McCarthy.
"This is a gift to Vladimir Putin, and it endangers American lives," McCarthy tweeted. "Leaving Paul Whelan behind for this is unconscionable."
Biden administration officials will remain in close contact with the Whelan family, the president said earlier.
"We'll keep negotiating in good faith for Paul's release. I guarantee that. I say that to the family. I guarantee you. I urge Russia to do the same to ensure that Paul's health and humane treatment are maintained until we are able to bring him home. I don't want any American to sit wrongfully detained one extra day if we can bring that person home," he said.
Whelan's twin brother, David, released a statement just ahead of Biden's remarks calling the swap for Griner "the right decision."
"As the family member of a Russian hostage, I can literally only imagine the joy she will have, being reunited with her loved ones, and in time for the holidays. There is no greater success than for a wrongful detainee to be freed and for them to go home. The Biden Administration made the right decision to bring Ms. Griner home, and to make the deal that was possible, rather than waiting for one that wasn't going to happen," he said.
He said officials let them know in advance "that Paul would be left behind," unlike in April, when news broke of former U.S. Marine Trevor Reed's return.
"This is the event we wish for so much for our own family," the Whelans said in April, and again on Thursday. "She will be reunited with her family. Brittney is free. And Paul is still a hostage."
A senior Biden administration official told reporters on a background call that another official had spoken "at length" with Whelan from prison to talk through the news of Griner's release.
"I want to be very clear: This was not a situation where we had a choice of which American to bring home. It was a choice between bringing home one particular American, Brittney Griner, or bringing home none," the official said.
Griner will be back in the U.S. within 24 hours, according to officials.
"She's safe. She's on a plane. She's on her way home," Biden said alongside Brittney's wife, Cherelle, Vice President Kamala Harris and Secretary of State Antony Blinken.
Blinken, in a written statement, praised Griner's release but lamented that Whelan and his family "continue to suffer needlessly."
"Despite our ceaseless efforts, the Russian Government has not yet been willing to bring a long overdue end to his wrongful detention. I wholeheartedly wish we could have brought Paul home today on the same plane with Brittney," Blinken said.
Former New Mexico Gov. Bill Richardson, who for months tried to help negotiate a trade for Griner and Whelan and travelled repeatedly to Moscow for meetings, said his team is thrilled Griner is now free but called for the Biden administration to now make Whelan's return a priority.
ABC News' Cindy Smith, Ben Gittleson and Justin Gomez contributed to this report.