The study, which was published in the journal Economic Inquiry, found that the effect of concealed carry laws on murder rates takes time to manifest but that it is negative and statistically significant in the following years. When you read "negative," understand that means concealed carry is reducing the murder rate.

Estimating The Effect Of Concealed Carry Laws On Murder: A Response To Bondy et al. Carlisle Moody & John R. Lott
The study was conducted using a sample of all 50 states from 1970 to 2018. The researchers controlled for a variety of factors that could affect murder rates, such as the unemployment rate, the poverty rate, and the incarceration rate.

The researchers found that the effect of concealed carry laws on murder rates is heterogeneous. This means that the effect of these laws may vary depending on the state or the type of law. For example, the study found that constitutional carry laws, which allow people to carry guns without a permit, may have a larger effect on murder rates than right-to-carry laws, which require people to obtain a permit (aka permission slips) to carry guns.

Lott and Moody write: "We find that the effect of right-to-carry laws on murder is negative but not significantly different from zero in the year of adoption. However, the effect becomes negative and statistically significant in the following years. This suggests that it takes time for people to get permits and start carrying guns, and that it takes time for the effects of this to be felt on crime rates."