Dzhokhar Tsarnaev, convicted of murder in the 2013 Boston Marathon bombing, was sentenced to death by a federal jury Friday. But if he is executed at all, it isn’t likely to be anytime soon.

In the nearly four decades since the Supreme Court reinstated the death penalty, the states and the federal government have taken an increasingly long time to carry out executions. The average inmate executed in 2013 had been on death row for more than 15 years, according to the Bureau of Justice Statistics, up from about six years in the mid-1980s.

And that’s just the people who end up being executed: Of the nearly 8,500 Americans sentenced to death in federal and state courts since 1973, fewer than 1,400 — less than 1 in 6 — have been executed. The rest either died of other causes, had their sentences overturned or commuted, or remain on death row, where inmates have been waiting an average of nearly 15 years.